If you go Alto, just make sure you get FULL thickness steels. You'll have less friction plates but you don't want to get thinner steels as they tend to warp. This is based on my research, I'm no trans builder.
As far as Z-pak, I bought my 99 GMC Sierra with 140K with the trans shot. The trans guy at my dad's dealer rebuilt it for me and I had him put in the Z-pak and it has performed flawlessly for 25K miles (have 165K now). I know a truck application is much different than a high HP car but I do a ton of towing with the thing and I've been very happy so far....we will see I guess. I'll be happy if it lasts 100K on the rebuild. I also had a wider 2-4 band, and Sonnex Super hold 4th gear servo as well as Corvette servo for second.